1. Field of the Invention
The present invention relates to a radio control method and radio control apparatus.
2. Related Background of the Invention
Non-patent Document 1 (3GPP Specification detail, 3GPP TS 25.331. [online]. version 6.10.0. [retrievedon 2006-09-07]. Retrieved from the Internet: <URL:http://www.3gpp.org/ftp/Specs/html-info/25331.htm>) and Non-patent Document 2 (3GPP Specification detail, 3GPP TS 25.308. [online]. version 5.7.0. [retrievedon 2006-09-07]. Retrieved from the Internet: <URL:http://www.3gpp.org/ftp/Specs/html-info/25308.htm>) describe the standard specification of the W-CDMA system, and Non-patent Document 3 (cdma2000 High Rate Packet Data Air Interface Specification. [online]. [retrievedon 2006-09-07]. Retrieved from the Internet: <URL:http://www.3gpp2.org/Public_html/specs/C.S0024-A_v1.0—040331.pdf>) describes the standard specification of the cdma2000 system. Furthermore, Non-patent Document 2 describes the specification of HSDPA (High Speed Downlink Packet Access) which is a high-speed downlink packet transmission system, and Non-patent Document 3 describes the specification of a high-speed downlink data transmission system (1xEV-DO). In the case of the W-CDMA system, a mobile station monitors the quality of radio communication with radio base stations (which is evaluated, for example, using CPICH-RSCP, CPICH-Ec/N0, pathloss, or the like indicating received signal power, which will be referred to hereinafter as radio quality, and which will be assumed to be based on CPICH-RSCP), and determines which should be performed, branch addition, branch elimination, or branch replacement, based on this radio quality. The mobile station notifies a radio control apparatus of this determination and the radio control apparatus performs control of soft hand over (SHO), based on this determination notified of by the mobile station.
A branch is a radio link between a mobile station and a radio base station and sometimes represents this radio base station itself. A collection of radio base stations (radio base station group) in radio communication through the use of SHO with a mobile station is referred to as an active set. The branch addition means adding a radio base station to perform communication through a radio link with a mobile station, to the active set. The branch elimination means eliminating any one of a plurality of radio base stations constituting the active set. The branch replacement means replacing a radio base station with the lowest radio quality among a plurality of radio base stations constituting the active set, with another radio base station which has a radio quality relatively better than that of the foregoing radio base station and which is not included in this active set.